Japanese prosecutors raided Olympus Corp units on Wednesday in connection with a huge accounting scandal that has threatened the existence of the 92-year-old maker of cameras and medical equipment, Japanese media reported.

A spokeswoman for the Tokyo district prosecutors office could not confirm the reports.

Tokyo prosecutors, police and the Securities and Exchange Surveillance Commission have joined in a rare joint probe of Olympus' 13-year, $1.7 billion scheme to hide investment losses stretching back two decades.

Prosecutors began raiding three units acquired by Olympus as part of the loss-making scheme, public broadcaster NHK said. Raids are expected later in the day at Olympus headquarters, it added.

A panel of experts appointed by Olympus to probe the scandal reported earlier this month that former Executive Vice President Hisashi Mori and ex-internal auditor Hideo Yamada masterminded the scheme with the help of investment bankers, and that three ex-presidents including Tsuyoshi Kikukawa had known about the cover-up.

Former Olympus CEO Michael Woodford, who blew the whistle on the scandal after being axed in October, is campaigning to get his job back but faces a potential proxy fight with management, who want to pick their own successors.